PROJECT SUMMARY/ABSTRACT In untreated infection, HIV-1 can establish populations in the CNS, often in long-lived myeloid lineage cells. Examining these tissue reservoirs in antiretroviral therapy (ART)-suppressed humans is rarely possible; creating a need for a nonhuman primate (NHP) model that recapitulates many of the features of NeuroHIV in humans. The objective of this study is to develop, and use, a novel simian-human immunodeficiency virus (SHIV) model to examine viral persistence in the CNS during ART and to determine whether CNS reservoirs contribute to viral rebound when ART is stopped. This model will generate CNS disease at a moderate pace, similar to that observed in HIV-infected humans, rather than the extremely rapid pace of most SIV models of NeuroAIDS. We have generated replication competent novel SHIV clones carrying eight different HIV-1 envs, each of which was cloned from either the human CNS, where it was adapted to replicating in myeloid lineage cells (M-SHIVs), or from the human blood, where it was adapted to replicating in CD4+ T cells (R5 T-SHIVs). In addition, we have incorporate newly discovered mutations in env that greatly increase SHIV replication in rhesus macaques. In vivo competition experiments will be used to identify SHIVs that replicate robustly and establish viral populations in the CNS within 1 year of infection (Aim 1). High fitness SHIVs will then be used to test the hypothesis that M- and R5 T-SHIVs are both able to establish reservoirs that persist during ART, but that M-SHIV reservoirs will primarily be found in the CNS, while R5 T-SHIV reservoirs will primarily be found in T cell-rich tissues (lymph nodes and gut) (Aim 2). We will then examine the contribution that these variants make to viral rebound after ART interruption (Aim 3). Successful completion of these aims will both establish a realistic model of HIV-1 CNS disease that can be applied to future studies of eradication and it will expand our knowledge of viral persistence in the CNS by identifying the types of infected cells that persistent during antiretroviral therapy and whether these cells persist as latent or actively replicating reservoirs.